650,000 years of greenhouse gas concentrations

The latest results from the EPICA core in Antarctica have just been published this week in Science (Siegenthaler et al. and Spahni et al.). This ice core extended the record of Antarctic climate back to maybe 800,000 years, and the first 650,000 years of ice have now been analysed for greenhouse gas concentrations saved in tiny bubbles. The records for CO2, CH4 and N2O both confirm the Vostok records that have been available for a few years now, and extend them over another 4 glacial-interglacial cycles. This is a landmark result and a strong testament to the almost heroic efforts in the field to bring back these samples from over 3km deep in the Antarctica ice. So what do these new data tell us, and where might they lead?

First of all, the results demonstrate clearly that the relationship between climate and CO2 that had been deduced from the Vostok core appears remarkably robust. This is despite a significant change in the patterns of glacial-interglacial changes prior to 400,000 years ago. The ‘EPICA challenge’ was laid down a few months ago for people working on carbon cycle models to predict whether this would be the case, and mostly the predictions were right on the mark. (Who says climate predictions can’t be verified?). It should also go almost without saying that lingering doubts about the reproducibility of the ice core gas records should now be completely dispelled. That a number of different labs, looking at ice from different locations, extracted with different methods all give very similar answers, is a powerful indication that what they are measuring is real. Where there are problems (for instance in N2O in very dusty ice), those problems are clearly found and that data discarded.

Secondly, these results will allow paleoclimatologists to really look in detail at the differences between the different interglacials in the past. The previous 3 before our current era look quite similar to each other and were quite short (around 10,000 years). The one 400,000 years ago (Marine Isotope Stage 11, for those who count that way) was hypotheisied to look more like the Holocene and appears to be significantly longer (around 30,000 years). Many of the details though weren’t completely clear in the Vostok data, but should now be much better resolved. This may help address some of the ideas put forward by Ruddiman (2003, 2005), and also help assess how long our current warm period is likely to last.

More generally, since the extra interglacials that are now resolved have very different characteristics from the previous ones, they may allow us to test climate theories and models over a whole new suite of test cases. To quote Richard Alley “Whether you’re a physicist, a chemist, a biologist, a geologist, or any other “ist” studying the Earth system, there is something in these data that confirms much of your understanding of the planet and then challenges some piece of your understanding”. It’s all very exciting (for us ‘ists’ at least!).

Update 1 Dec: Thomas Stocker sent in a better figure of the composite results for CO2, CH4, and the isotopes: .

122 Responses to “650,000 years of greenhouse gas concentrations”

Your graph is not very lisible.
Can you rectify it?
A question:
Is this time of -800000 years the possible limit of ice cores?
And what is the becoming of very much older ice in Antarctica or Greenland?
I suppose these both regions were cold since millions of years.
So is there a sort of melting of very deep ice in contact with ground and under pressure?

One little annoying thing is that looking at the graphs quick makes you think that what’s happening now is nothing new and has happened before (the fast changing temperature)… are there good explanations for all the peaks? (Bet there are…)

To be a bit more precise, the correlation between CO2 and temperature has been known for quite some time, and this just makes it stronger. The early (and some times still) question is what comes first, and there is no one line answer to that…

Discussing the anthropogenic effect of the temperature this correlation would help if you clearly could say that CO2 affects the temperature an not only the other way around. Now looking at the graphs it mainly looks the other way around. And explaining that it some times before CO2 also strengthens or weakens the temperature effect isn’t all that easy?

So what would you say to a person that shows this diagrams and says, look it is the temperature that affects CO2 not the other way around. And if he continuous to argue that it have bean really fast changes in temperature before and it don’t have anything to do with CO2…

To #3
The question on the phaselag between CO2 and temperature was answered several times already, e.g. http://www.sciencemag.org/cgi/content/full/283/5408/1712 find a lag of about 600 years during glacial terminations. Among many other factors the ocean has an important control on CO2 concentrations which is why a phaselag of a couple of hundred years is no surprise. During the change from cold glacial to warm interglacial conditions it’s not CO2 which is moving first and somehow driving primarily the system.
To your second question: The real question is if you can understand the global character of glacial endings and the corresponding temperature amplitudes without a CO2 feedback. The answer is no. This results is based on different type of model studies.
The curves therefore give you an idea of how CO2 and temperature are linked to each other by different mechanisms acting on different time scales.
To find out what triggered the end of a glacial is however a different story and I dont see that CO2 should be the driving agent as your question suggests.

Any comment on this story in the Guardian today. In particular there’s the somewhat misleading sub-headline “Cut in greenhouse gases futile, researchers say” which implies that even if we did cut emissions massively it wouldn’t make any difference.

From what I know I thought that significant differences would be seen by the end of the century if you compare a stabilistion scenario at 450 ppm and a ‘business as usual’ scenario where CO2 levels keep rising through 2xpre-industrial [550ppm] and keep on going higher.

If you dig a bit deeper into the text of the article it turns out that the Professor is saying the he doesn’t think that GHG emissions will be cut enough to make a difference which is a different thing altogether. [ie he thinks that *if* CO2 emissions were cut by ~50% then it would make a difference but he doesn’t think that such a cut is politically or economically feasible].

[Response: Miller’s point is that sea level will continue to rise under any conceivable scenario (as seen in the ‘committed climate change’ papers by Meehl et al and Wigley earlier this year. The sub-headline is misleading though; while cuts in emissions will not prevent sea level rise, they may prevent the worst case scenarios in the medium to long term. -gavin]

#1
800Kyr must not be the absolute limit. I think Dome A is discussed of being a possible drilling site with ice going back until 1,000ky BP. Quality of DomeC ice at the bottom is already poor and I dont know about the future of gas measurements in the lowest part.
In Greenland the search for a place nicely stratified down to the bottom goes on. The is the discussion about North North GRIP looking for a place covering the Eemian period (130.ky). Much older datable ice is very improbable to find there.
Yes there is underground melting both in Greenland and in Antarctica. Check for Lake Vostok and corresponding scientific activities to drill this lake (mainly to learn about its biology). More fantastic projects include drilling into the lake sediments of Lake Vostok thereby having access to climate information over a couple of millions of years.

I know the C budget and it’s ways through the system. My thought was that maybe some one has a good quick answer to some old historic passage where CO2 clearly (seem to) have an effect. I’m just pointing out what I hear regularly from what persons that are new to these things say.

However I also know that there seldom is a quick answer to complicated issues…

Thanks for your response Georg.
How can we understand the relatively abrupt increasing of CO2 concentration after glacial period?(less abrupt than now)
Can orbital oscillations (Milankowitch) be so discontinuous?
Or can we invoke retroactions or volcanic CO2?
Do climate models offer us good simulations of these periods?

Somehow the ice cores are getting back into the attention. I predict that the isotope (=temperature?) and CO2 correlation is the biggest misunderstood phenomenon in the whole climate science.

Once it will be clear what we can really see in the ice cores and it has nothing to do with warming.

I posted this somewhere else today:

Not Temperature but Precipitation (Non Calor Sed Umor)

The other month I posted this:

“The isotope spikes in the ice cores are not temperature indicators but precipitation indicators. Of course I know that lesson one part A of climate theory is that ice cores store temperature changes in oxygen and hydrogen isotope ratios (d18O and dD), but it’s very easy to proof that this is not true. Both on the long time scales ~420,000 years (Vostok and EPICA Dome C ice cores) as for the detailed millenium scale around the last termination (GRIP, NGRIP, GISPII ice cores). Multiple palynological proxies are showing clearly that the Younger Dryas was not cold but dry and that the start of the Holocene was not warming but a dramatic, perhaps near global, increase of precipitation. Moreover it can be shown that the increase of humidity reduces the Rayleigh effect which leads to a increase in heavy isotopes (18O, 2H), misinterpreted as warming. Furthermore an increase in summer precipitation has the same effect, increasing the average ratio of heavy isotopes, without a requirement for warming. Bottom line, those “isotope = temperature” graphs are not temperature but precipitation changes and for the last five “glacial terminations” in the last half a million years we may very well have found what has caused it exactly: the country size clathrate destabilisation that caused and preceded the giant Storegga landslides at the slope of the European continental plate between Norway and Iceland.(Bryn et al 2005). The last event (Mienert et al 2005). led to the extinction of the mega fauna (Mammoths, Mastodonts, etc). The mechanism: strong increase in oceanic evaporation due to effective ocean surface enlargement (bubbles, splash water) due to roiling of the methane gas and a strong surface water current radiating away from the event, disrupting normal patterns and sending warmer water to arctic areas

********** So Did I mention what caused those CO2 spikes?

Picture that methane roiling in ocean also sending deep waters to the surface. Deep water is under high pressure and can contain (much) more CO2. So when the pressure is released at the surface, just like opening a coke bottle, the CO2 comes sizzling out escaping into the atmosphere. That’s why the CO2 spikes in those ice cores lags the isotope spikes slightly.

Upon seeing the host author, I know already that the rebutal will be for my post, that doesn’t show yet. Yes I’m familiar with the d15N/d40Ar behavior during the Bolling Allerod and PreBoreal spikes in the Greenland Ice cores. I’m also familiar with several palynologic studies that contradict the d15N d40Ar = temperature conclusion but support the precipitation hypothesis.

The question is what a dramatic increase of summer precipitation and it’s inclusion of warmer summer air in the snow would have on the d15N d40N.

[Response: Since you already know why you are wrong, it seems superfluous to mention all the other lines of evidence: increased % pachyderma in N. Atlantic sediments, higher d18O calcite in foraminefera, alkenone measurements, diatom assemblages, etc. etc… but I can’t help myself. Plus, ‘dry’ and ‘cold’ tend to go together in N. Atlantic region climate changes, so evidence of one is not evidence of the absence of the other. -gavin]

[Also, Gavin didn’t mention the beetle data from English bogs, showing Younger Dryas was not just cold, but that the mean annual cooling was especially in winter. These data are at least 20 years old and precede the ice core N-isotope data (and entirely agree with it). — eric]

According to EPICA, they drilled until they were 5 m above bedrock. Their limiting factor was the ice thickness at the drill site. One may therefore assume that thicker ice would allow for older ice cores.

[Response: In fact the Vostok core is deeper than the EPICA core: http://en.wikipedia.org/wiki/Image:Epica_do18_plot.png but doesn’t go so far back in time. What you need for a really long-time core is an ice dome (so no/minimal flow) and a low accumulation rate – William]

Gavin have you wondered why the oceanic sediment proxies respond so promply on the isotope spikes whilst the oceans behave like a slow higher order response system with eigen frequencies of centuries to millenium. Have you seen that the oceanic proxies actually seem to be leading the ice cores instead of lagging. Have you wondered why all those articles are full with unknown and “not understood”. Any idea what changes in salinity, p02, pH would to do benthic proxies? Any idea what massive clathrate destabilisation events would do to salinity pO2 pH etc but most of all the changes in response characteristics?

It’s all part of the puzzle, that could not be solved before knowing the complete picture.

re #11: Independent evidence that the oxygen isotope records are a reasonable proxy for temperature comes from temperature measurements of the ice made during the drilling of the core. The borehole temperature measurements confirm the interpretation of changes in oxygen isotope records as fluctuations in surface temperature.

re 15
The borehole temperatures (Greenland GRIP and GISP-2) are far too indistictive to show the Younger Dryas let alone other spikes. They make it clear that it has been colder 20-30Ky+ ago but you cannot find the border on that very shallow graph. It does not show when exactly the jump to warming happened.

Consider this, the last glacial maximum was 18-22 carbon years ago (22,5-27 Ky cal Bp) after that many glacial proxies in America showed consideral warming and glacial retreat. But not a single indication in the isotope values. You had to wait to 14,700 Cal BP years (Bolling event), before there was any reaction. But together with the isotopes also the CH4 spiked as well as the precipitation in concert with all the next spikes, Bolling – Older dryas – Allerod – Younger Dryas – Pre Boreal. So if the great melting started earlier, confirmed by sea level proxies, to start at 19 Kyrs ago, why don’t we see the Last Glacial Maximum back in the greenland Ice cores? Why those late reactions?

[Response:It is indeed often said that the Greenland ice cores show a “late” deglacial signal. This is rather careless though, and not actually supported by the evidence. In fact, the Greenland isotope records have a minimum around 20 ka, just like the Vostok and other Antarctic ice cores do. Superimposed upon that are the higher frequencies ups-and-downs of the D-O events, which allow one to subjectively state that one has to “wait until 14.7 kyr B.P.” for the deglaciation to begin. But the ice sheets can only respond significantly to low frequencies, so it is the low-pass filtered version of the Greenland records you want to look at. And they look pretty much like Vostok. See e.g. Alley, R.B., E.J. Brook and S. Anandakrishnan. 2002. A northern lead in the orbital band: North-south phasing of ice-age events. Quaternary Science Reviews, 21, 431-441. — eric]

[Response: Sorry about that. The figure shows a composite record of CO2 measurements from 0 to 650,000 years ago (last section is from the new paper), along with the deuterium measurements from Vostok and EPICA Dome C. – gavin]

Re #1: To see the detail on the graph, click on it to open it in its own window, then zoom in as needed.

(Gavin, I have a different problem, which is that the top of the second paragraph is somehow cut off by the graphic. The first line I can see begins with “Vostok core appears…” I’m running Windows Explorer on XP Pro (both up-to-date) and have a 15″ monitor, if that’s any help. I’ve noticed this same problem on a couple of prior RC posts.)

I would welcome any sensible challenge to the following comments.
After reading the leading article, I conclude:
– there is a strong correlation between global temperature and global CO2 concentrations;
– Neither the article, nor referenced documents, provide any indication on whether temperature influences CO2 or vice versa;
– the results do not help us predict future world climate;
– The statement: “who says climate predictions can’t be verified?” is misleading in that it implies that the quoted results back ‘climate models’. On the contrary, the predictions apply to conditions with zero human influence and provides no indication on the impact of manmade CO2 emissions on future climate.

[Response: I’ll step you through it. There is a clear correlation between CO2 and temperature (and Milankovitch forcing). Given the lag in CO2/CH4 to Milankovitch and temperature it is clear that climate influences CO2 and CH4 levels. Given separate studies in how cold the planet was at the peak of the last ice age given those values of GHGs and ice sheets etc. it is clear that GHG forcing is roughly reponsible for half of the glacial cooling (e.g. Lorius et al, 1990). Thus we have a classic feedback – climate influences GHGs (through ocean + biosphere interactions), and GHGs in turn influence climate (through the atmospheric greenhouse effect). If, given the Milankovitch forcing and how warm it was, carbon cycle models can correctly estimate how much CO2 was in the atmosphere, prior to the actual results being released, it implies the carbon cycle models have some skill at relating the three effects. And finally, since the atmosphere doesn’t care whether CO2 is man made or not, and given that Milankovitch forcing is small for the next few centuries, the same physics will likely work for the future as well. -gavin]

Quote:
Here we demonstrate the possible use of the fossil remains of beetles in the weevil genus Stephanocleonus for Late Pleistocene and Holocene climate reconstruction.

“.that they feed on only a few species of plants and occupy habitats, with a relatively narrow range of environmental conditions.”

“The main range of these species is zonal steppe and mountain steppe of southern Siberia and Central Asia. As in the case of the weevils,

Three weevil species – Stephanocleonus eruditus, S fossulatus, and S. foveifrons, play important roles in the insect fauna of relic steppe biotopes. “.

The Pleistocene remains of these weevils have been discovered throughout northeast Asia. Stephanocleonus fossulatus and S. eruditus were common throughout the immense area from the Lena River to the Anadyr River; fossil remains of S. fovifrons have been found in the lower reaches of the Kolyma and the Indigirka and on Ayon Island

I would just like to add to Gavin’s reply that from basic physics we know that CO2 in the atmosphere exerts a direct warming influence (it helps trap infrared radiation). One of the things that the paleoclimate record tells us is there are no natural feedbacks in the climate system that will serve to entirely negate warming due to the CO2 and other GHSs we are adding to the atmosphere. This picture is also consistent with the fact that no one has ever came up with a physicaly plausible climate model (here meaning the full range from complex GCMs to simple “back of the envelope” conceptual models) that predicts that adding more GHGs will not raise the global mean temperature.

I’ll second Gavin’s comment regarding #19. The LGM situation provides the most direct evidence against the existence of some unanticipated stabilizing feedback that would ameliorate the response of climate to CO2 (e.g. Lindzen’s old cumulus drying idea, or his newer Iris idea). If such a mechanism existed, it would almost certainly work during LGM times as well as in the present. If that were the case, then the implication would be that models (without this mechanism) exagerate the cooling due to reduction in CO2 in glacial periods. However, WITH the CO2 effects, current models can come close to reproducing the observed degree of cooling. If some strong stabilizing feedback were added to the models, then they would NOT be able to reproduce glacial-era climates.

Study of the LGM gives a pretty strong indication that the range of CO2 sensitivity in the IPCC models can not be too far off the mark. There’s a lot of work underway now to tighten up this statement, so as to use the LGM behavior to provide some indication about whether the true climate sensitivity is near the lower or higher end of the IPCC range.

I’ve seen the contrarian argument before regarding warming preceding increases in GHGs, with the implication that this disproves AGW. I’m no climate scientist, but simple logic tells me this in no way serves to disprove the point that GHGs cause warming (the two are analytically separate issues) — and this latter has been well accepted for a long time re the natural greenhouse effect. The only issue remaining was whether the addition of our human GHGs could cause additional warming, and that has been long resolved enough for me to turn off lights not in use.

However, the idea, which contrarians seem to embrace whole-heartedly, that warming precedes (and thus causes) an increase in GHGs, is a very serious issue indeed, and points to the possibility of runaway global warming (positive feedback loops), which would make global warming all the more serious, by contrast to only GHGs causing warming. What it means is that my GHG emissions may have much worse repercussions — the harm that keeps on harming and harming and harming. (I don’t think this positive GHG-warming feedback loop is included in the “sensitivity” factor/calculations re human GHG emissions, but if it were or could be, then we’d be talking a much higher order of sensitivity.)

I wish some sincere policy-makers more concerned about people living the world than corporations amassing huge bank accounts in the very short run are out there reading about this serious issue, so that we can quit stalling and put forth massive efforts to reduce human GHGs — which by contrarians’ own admission are much more dangerous than merely causing increased warming (as previous thought), but that increased warming then causes increased GHG emissions, which cause further increased warming, which causes further increased GHG emissions, which cause….an so on.

The emperor is really wearing no clothes on this one. Contrarians better stick to the current fashionable cloak that AGW is happening, but it’s cheaper to adapt to it than mitigate it (I also have my arguments against that, as well).

Re: #24, “The emperor is really wearing no clothes on this one. Contrarians better stick to the current fashionable cloak that AGW is happening, but it’s cheaper to adapt to it than mitigate it (I also have my arguments against that, as well).”

Forgive me for injecting a tiny bit of black humour amongst the gloom into this discussion. If we keep to a business-as-usual scenario, we may all be joining the emperor and be wearing no clothes, as well, since it may be far warmer in the future and many of us won’t be able to tolerate the heat.

I thank Gavin for addressing my questions (no.19). However, I do not feel they are answered. Yes, there is a very strong correlation between historic temperature and CO2 concentrations, which seems to explain the success of predictions on the core results. I presume the reason for discussing the study was that it is assumed to support the case for AGW. I just don’t see this, but am happy to be enlightened. What am I missing? Milankovitch is not mentioned in the article or any of the links, so I don’t see why “he” is so significant in the response. My main point is that I do not see how the quoted study contributes to the case for AGW (regardless of what ‘separate’ studies may show).

Re #27: The graph in question is on a scale of thousands of years. The rise in carbon dioxide levels from 270 ppm to 370 ppm in the last hundred years simply does not show on such a scale. This rate of increase is unprecedented (200 times as fast) for the time period of this graph, and clearly has a different cause than the Earth’s orbital variations. Global warming theory is not contradicted in any way by this information.

You don’t have any ice core data that shows 380ppm.
You have Mauna Loa, but that is not really comparing apples with apples, is it?

[Response: I have Law Dome which overlaps and matches both Mauna Loa and the other pre-industrial ice core data. Highest value measured in an ice core 323 ppm, corresponding to around 1969 levels. So even the pure ice core data show values higher than any seen in 650 kya. -gavin]

This new ice core data has recieved much more media attention than the Vostok ice cores did when that ground breaking research was made public. Perhaps Katrina, and all the other storms this year will be marked as a tipping point that led to the American media waking up from the “some scientists” trance that they’ve been in for 10 years.

My question is: If one were to still be doubtful of the reliability of climate models and wanted to extrapolate from the ice core data, what result would today’s and projected greenhouse gases give?

Law Dome, the one where the age of the air is adjusted by 30 or 58 years depending, but not the 83 years like Siple?

You know it’s hard to believe that air and ice and CO2 can behave so differently, and yet the one thing that remains constant in all this is that the adjusted CO2 data from the latest ice cores always matches exactly the starting data from Mauna Loa.

“I recently visited Hawaii and observed the Mauna Loa site, and this has convinced me that measurements of carbon dioxide from that site are not indicative of “the well mixed background.” Mauna Loa emits carbon dioxide and is adjacent to Kileaua (the most active volcano on Earth). It seems very likely that Keeling’s carbon dioxide measurements are significantly affected by variations in emissions of carbon dioxide from Mauna Loa and Kileaua together with wind direction relative to Kileaua. Indeed, Keeling adjusts his data for effects of Mauna Loa activity and deletes data from his time-series for the periods when Mauna Loa was especially active (of itself, an admission that his data are not direct measurements of “well mixed background”). But his reports do not mention any adjustments made for effects of Kilaeaua’s activity.”

In November 1998 I had correspondence with Dr Curtis Covey (an IPCC author) concerning my severe doubts at the ice-core data. Referring to my dispute that it was correct for the IPCC to have transposed the ice-core data by 83 years, he said;

“… such displacements might be considered a somewhat arbitrary calibration that diminishes the significance of the fit between ice-core and modern measurements. At last week’s IPCC meeting I raised this general question with Haroon Khesghi of Exxon. Haroon referred me to Fortunat Joos of the University of Bern, who told me that this calibration is no longer used in recent work, and yet the remarkable agreement between ice-core and modern measurements continues.”

and more:

“I responded that I did not accept the 83 year transposition was acceptable. Diffusion occurs from regions of high to low concentration and, therefore, incomplete sealing of snow over an 83 year period would act like an 83 year running mean; it would not transpose all the carbon dioxide a similar amount in one direction. Also, if the IPCC has stopped using the transposition, what correction method is now used? And when will the IPCC publish this newly corrected data in place of the graph of historic atmospheric carbon dioxide concentration that it published in both its 1992 and 1994 reports ? I received no answer to these questions.”

[Response: Funny stuff. Generally speaking cutting-and-pasting from the wackier of the sceptics sites is not a very credible line of argument, but let me take this as a teaching moment. Law Dome and Siple Dome have different accumulation rates (which are much higher than from Vostok or EPICA). Air mixes through the firn down to the depth at which bubbles are closed off. Therefore new air is trapped in ice that is significantly older. This depth occurs in ice of different ages – i.e. younger ice in higher accumlation cores, and this leads to the ‘ice-age/gas-age’ difference, which will be different in different cores (it would be ‘spooky’ only if it were the same). This age difference has nothing whatsoever to do with the filtering of the atmospheric CO2 concentration – that instead is related to the strength of the wind-pumping in the firn and the process of bubble formation and is much much shorter (around 20 years). Oh and by the way, the Mauna Loa record started in 1957 when CO2 was only around 315ppm, and shows almost the same annual values and trend as the South Pole data started at the same time. Spooky that…. -gavin]

Re #30: I don’t mean to pile on (much anyway), but strictly speaking those would need to be snow core data to show 380ppm. :)

Re #31: Mark, we are putting a bunch of CO2 into the atmosphere very quickly indeed. Nature doesn’t do that. Ironically, the current rate of CO2 increase has been described by at least one skeptic site as so small as to be trivial. It’s all a matter of what you’re comparing it to, I suppose.

Can anyone direct me to references which describe how EPICA deals with the storage and transport of ice cores to analytical labs in Europe? I am particularly interested in steps they took to reduce ambient air contamination. The earlier EPICA article does not address this.

[Response:There were a bunch of studies, some 20 years ago, looking into the possibility that CO2 concentrations in ice cores change with storage and transport of cores. The findings are that as long as the cores remain below -10C (which all of us who work with ice cores lose sleep over, and are very careful about), there is no measureable change, even after many (10+) years. Consequently, for gases, the major concern is simply the preservation of the ice at cold temperatures, and the avoidance of breakage. I doubt the EPICA folks have bothered to publish anything new on this, as it is all very well established protocal, which is why the papers you are looking at don’t address it directly. You can no doubt find references to the methods for CO2 measurements within the references sections of the papers though. I’ll take a look and get back to you on this site. Basically, the rules are: keep it frozen; do your analyses on ice that is in the center of the core, after removing the outer part of the core, to miminize any possible contamination that might result from handling.–eric]

Where is the supposed “water vapor feedback” in the ice cores temperature record? As CO2 concentrations rise, aren’t we supposed to see a magnified effect on global temperatures because the GHG warming is supposed to cause the atmosphere to hold more water vapor?

Re: #37, “Where is the supposed “water vapor feedback” in the ice cores temperature record? As CO2 concentrations rise, aren’t we supposed to see a magnified effect on global temperatures because the GHG warming is supposed to cause the atmosphere to hold more water vapor?”

This may be identified by the thickening of Antarctica and Greenland’s existing ice cap, as a result of increased precipitation due to surface temperature and SST increases.

As for a “‘water vapor feedback’ in the ice cores temperature record”, water vapour cannot be identified in ice cores since the water vapour condensed and precipitated, allowing the annual layers of ice to form.

After carefully matching the CO2 gas age to the nearest ice age, the change of CO2 is some 8 ppmv for each change of 1 K in reconstructed temperature (or vv.) for the Vostok ice core over the full 420,000 years period, see regression here. The Dome C record seems to confirm this correlation between CO2 and temperature.

About the chicken-and-egg question, there is little doubt that in the Vostok ice core, there is a lag of several hundreds of years of CO2 after the start of the temperature increase during a deglaciation and several thousands of years after the start of a glaciation. See: Fischer ea.. For more recent time periods, before the industrial revolution, I have only found lags of CO2 after temperature changes: for the 60-20 kyr BP period in the Taylor Dome ice core, for the Younger Dryas event (comment on stomata data, not on the Net anymore), for the past 1,000 years (Law Dome, a lag of app. 50 years after temperature changes – temperature data not available in the Law Dome database).

But in many cases, there is an overlap of temperature and CO2 trend changes. That is e.g. the case for all deglaciations, where the lag is 600 +/- 400 years, but the total transition period is some 3,000 years.

There is one exception in the whole Vostok trend: after the onset of the last glaciation (some 120,000 years ago), the CO2 levels remained high, until the temperature was near its minimum, before CO2 levels started to decline (see trend and data at NOAA. There is no measurable influence from a change of 50 ppmv CO2 on temperature, while, according to climate models, halve of the 6 K cooling (and thus also for a 10-12 K warming during deglaciations) should be attributed to the change in GHGs (and their feedbacks).

[Response:This analysis is out of date. First, while the CO2 data are very precise measurements of exactly what is of interest (CO2 concentrations), the stable isotopes provide only a fuzzy estimate of temperature. This has been looked at very carefully, and the best evidence (Cuffey and Vimeux, Nature, 2001) shows that the supposed lag at 120,000 is an artifact of the changing relationship between isotopes and temperature. Their calculations pretty much kill of this much-loved example of the climate change skeptics — eric.]

The lag of CO2 is probably not an artefact of problems with matching of ice age with gas age, as CH4 (methane) levels more closely follow the temperature trend. Neither does the recent correction of the reconstructed temperature by Jouzel ea. (last page) change the timing of the events, only the amplitude of the temperature trend is changed.

This doesn’t mean that the CO2 increase in recent times has no influence on temperature, only that relative small changes in CO2 level have no measurable influence on reconstructed temperature from ice cores, and that current models probably overestimate the influence of CO2 (+ feedbacks) and thus probably underestimate solar influences.

#39 Points out..”This doesn’t mean that the CO2 increase in recent times has no influence on temperature, only that relative small changes in CO2 level have no measurable influence on reconstructed temperature from ice cores, …” I am not sure what small changes are in your mind but in recent times we are hardly talking about small changes in CO2 levels as noted by Thomas Stocker “We find that CO2 is about 30% higher than at any time, and methane 130% higher than at any time; and the rates of increase are absolutely exceptional: for CO2, 200 times faster than at any time in the last 650,000 years.” Look at how slowly CO2 rose at the end of each glacial period compared to now. In the Dome C core EPICA 17,000 BP it was 190 ppm and took 5400 years to rise to 250 ppm.

For scientific purposes the graph is excellent and exciting; for public communication purposes it could be better.

Al Gore drew the anthropogenic CO2 perturbation on a 100KA graph in his book Earth In The Balance. Al Gore is a politician, not a scientist. In this case, I don’t intend that as a criticism. Politicians’ skill is to communicate to a very broad range of people.

There is an extraordinary spike in CO2 that is essentially vertical at the present century on the scale of the graph shown. It would already double the range of the graph. It’s not shown on ice cores because it’s too young to appear in ice cores.

Comment #27 shows how thoroughly misunderstood the GHG situation is, and how eager some people are to misunderstand it. A helpful thing that realclimate could do in this case would be to publish the graph with the addendum of the observational record.

The CO2 measure from the ice cores is an estimate. There is no actual data from prehistoric periods. The Vostok and other samples may be useful in showing long time scale fluctuations, but they are not absolute evidence of the actual CO2 level at any time.

The CO2 measurements from Moana Loa and the others depend on the accuracy of the measurement, and the equipment used. As many people have commented, the relative change in detected CO2 is very rapid, and not explicable in terms of any naturally occurring phenomena.

Therefore, look at the actual collection and calibration of the CO2 data.

It has been pointed out that there are several sites measuring CO2, but the oldest is Moana Loa.

I was interested to find that the Moana Loa measurements from 1991 to 1996 have recently been re-calibrated.

WMO/IAEA Experts Meeting Boulder 19-22 September 2005

Revision of the international calibration scale for CO2-in-air: WMO-X2005.

Also that “….that there has been no drift of the mole fraction, cannot be rejected for any of the Primaries with the statistics we have.Therefore, we assume that,there has been no drift until now, and the assigned value for each primary is the average obtained for that cylinder during all CMDL calibration episodes. The above does not imply that the defined WMOScale has not drifted“.

…”In June 2002 CMDL received revised numbers from Scripps for the four calibrations by them of our fifteen WMO Primaries that they had carried out from 1991 to 1999. Their revised scale was called X99A.”

…..”Based on the assumption that the fifteen WMO Primaries have been stable, we have re-assigned a constant value (the average of the measured values during the six CMDL calibration episodes) to each of them going back to 1994. We call this revised scale WMO-X2005.”

I doubt if anyone can say any of this data is robust enough to make billion dollar life changing decisions on.

[Response: Hmmm… serious stuff. A revision of the scale based on better absolute measurements. And how much is this difference? a maximum of 0.16 micromol/mol. – In a more usual unit, that is 0.16 ppmv, compared to an observed change since 1957 of over 60 ppmv. So less than 0.3% error…Hmm. – gavin]

The statement that CO2 levels today are higher than those found in the ice cores,highlighted in the press, ignores the effect of long term diffusion which would have the effect of lowering and smoothing out the peaks. It is noticeable that the peaks and troughs are less sharp in the older data. I have failed to find data on the diffusivity of CO2 in ice, apart from comments on the effect of partial consolidation, the so-called time lag effect.It is probable that diffusive spreading has smoothed the concentrations to some extent, and raises doubts about statements about exeptional levels and rates today.

[Response:The smoothing you see is because of the thinning of ice layers through time, so that for each fixed amount of ice in a sample, it represents a longer amount of time. Higher resolution data is possible, but as seen in Delmotte et al, 2004, for Vostok, that increases the amount of variability, but does not affect the long term means seen in the current data. -gavin]

“The calibration shall consist of a determination by the Scripps manometer of the mole fraction of CO2 in each NOAA reference gas cylinder…”

“…it is the intent of the Government to award a sole source contract under the authority 41 U.S.C. 253 (c)(1) to the University of California at San Diego. Scripps Institute of Oceanography, 2314 Ritter Hall, LaJolla, CA 92093, as this source is considered to be the only responsible source and no other type of supplies or services will satisfy agency requirements.”

Not only were Scripps AKA Moana Loa the only collector of data, they were the only calibrator of the equipment.

If Scripps was wrong, then there was no independent check of the calibration, because they did it themselves, and all the other later CO2 measurers presumably had their equipment calibrated from Scripps.

The average increase Moana Loa measured was 1.3 parts per million by volume. That is 0.00013%.

Anyone confident that their measurements and calibration errors weren’t responsible for that?

[Response: Yep. since the calibration uncertainties are an order of magnitude smaller, plus they are uncertainties on the absolute scale – uncertainty in a difference between two samples is much smaller. You are really grasping at straws here. -gavin]

All depends of the influence of CO2 (and other greenhouse gases) on temperature (and in the case of CO2 on ocean pH and carbonate level).
From the ice cores we can learn that a temperature increase of 1 K is correlated with a CO2 increase of 8 ppmv. Thus the current temperature increase since the LIA (0.2-1 K, depending on the chosen reconstruction) is only responsible for a small portion of the near 100 ppmv increase in CO2 since the start of the industrial revolution.
The direct influence for a CO2 doubling is some 0.68 K (or 0.23 K for the current level), based on its absorption bands. All the rest is feedbacks, of which water vapour is the main positive response. But clouds (depending on thickness, height, season, latitude) seem to give a general negative response. That makes any projection of the climate models rather problematic, as clouds are the main origin of the large variation in range for a CO2 doubling.

As the start of the last glaciation indicates, if the influence of 50 ppmv CO2 + feedbacks is not measurable (direct influence: some 0.12 K, which is within the measurement error margins), that points to an overestimate of the feedbacks in most of current models. The real influence of a CO2 doubling on climate thus probably is at the low side of the IPCC range…

If I recall correctly Andre, you spent a considerable amount of time on the BBC boards attempting to tell me that the Younger Dryas wasn’t all that cold after all. I pointed you in the direction of a number of multiproxy studies that showed you to be wrong. Have you looked up the Gerzensee and Krakenes articles yet? I guess not.

Oh and if you are ever in the UK, why not pop over to East Anglia. We have Younger Dryas age sites, in southern England, that have evidence for frost shattering. I’m no periglacial expert, but I think this means it was pretty cold. As I told you last time.

It was cold here in the Younger Dryas. End of story. The only way you can argue otherwise is by cherry picking the odd study that suggests a slightly more complex spatial response.

Oh and while I remember, we had ice sheet growth in Scotland and Wales during the Younger Dryas. This tends to occur when its cold. I recommend checking out the literature. Its only been around since the 1920s.

#44 A study (van Hoof et al., Tellus, 2005) on the D47 core claims a possible short term diffusion effect of about 20ppm (short term CO2 amplitude hidden by firn diffusion) depending on accumulation and temperature. The recent 80ppm raise is very hard to hide in ice cores if this is what you suggest.
Georg